nosy person; busybody; insatiably curious person
Describes someone who always wants to know everything about others or about any topic, often to an annoying degree. Can be used lightheartedly or critically.
She's a real busybody, always trying to pry out people's secrets.
My little brother is insatiably curious and asks 'why?' about everything.
Compound of 知りたがり (wanting to know, from 知る 'to know' + たがる 'to want to') and 屋 (suffix for a person with a certain trait).